I’ve been playing around with the new common controls that are
distributed with IE 4.0 and one of the neat features is the new style
TVS_TRACKSELECT. Basically what it does is underline the current item
and then select it if you leave it there long enough. Now to me this is
annoying. I don’t mind it telling me where I am but selecting it
automatically for me I don’t like ( mainly because most trees I’ve seen
do something when an item is selected ). So I implemented hot tracking
in a CTreeCtrl derived class. Hot tracking is basically underlining the
item you are on, but not selecting it.
I was going to implement a state and then stick it in the LPARAM, but I
decided to use a state flag instead. So I defined this flag…
#define TVIS_UNDERLINE 0x0001
Now you might be wondering why I used 0x0001, believe it or not, this is
the only available state flag left to the tree control. It might be
used internally, but I have seen no side effects.
The first thing that must be done is setting the state of the item…we
do that in OnMouseMove…shown here…
void CTreeCtrlEx::OnMouseMove(UINT nFlags, CPoint point)
{
TV_HITTESTINFO hit;
::ZeroMemory(&hit,sizeof(hit));
hit.pt = point;
HitTest( &hit );
//Did we hit an item??
if( hit.hItem )
{
//Yep...now check to make sure we hit on the item not beside it
if( hit.flags & TVHT_ONITEM )
//Yep...underline it...
SetItemState( hit.hItem, TVIS_UNDERLINE, TVIS_UNDERLINE );
else
//Nope we sure didn't...since we might have
//moved the mouse to left or right after
//underlining it previously...go ahead and undo
//the underlining
SetItemState( hit.hItem, 0, TVIS_UNDERLINE );
}
//Must unconditionally check the last item or underline will stay around
// after we move off the last underlined item...
if( m_htiLast != hit.hItem )
{
SetItemState( m_htiLast, 0, TVIS_UNDERLINE );
}
//Cache the last item hit...
m_htiLast = hit.hItem;
UINT uID = SetTimer( MOUSE_MOVE, 55, NULL );
ASSERT( uID == MOUSE_MOVE );
CTreeCtrl::OnMouseMove(nFlags, point);
}
There ya go…item is now ready to be underlined. Now…you might be
asking…what happens if the first visible item ( which I define as
being right at the top of the control )is underlined and my user moves
the mouse out of the client area? Won’t the item still be underlined?
The answer – yes it will…unless you tell it not to 🙂
There are 2 ways you can tell it not to hilight the last item
underlined…
1) handle WM_NCMOUSEMOVE and undo the underlining of the the item if you
move over NC area.
2) Start a timer in WM_MOUSEMOVE ( I actually did both. You know…just
to make sure…) and check the point of the message. If it is in the
rect…do nothing. If it isn’t in the rect…loop through the visible
items and setting the underline state flag to 0. Here is my
implementation of both WM_NCMOUSEMOVE and WM_TIMER.
void CTreeCtrlEx::OnTimer(UINT nIDEvent)
{
if( nIDEvent == MOUSE_MOVE )
{
KillTimer(MOUSE_MOVE);
CPoint pt(::GetMessagePos());
CRect rc;
GetWindowRect(&rc);
if( rc.PtInRect(pt) == FALSE )
{
HTREEITEM hti = GetFirstVisibleItem();
while( hti != NULL )
{
if( GetItemState( hti, TVIS_UNDERLINE ) & TVIS_UNDERLINE )
SetItemState( hti, 0, TVIS_UNDERLINE );
hti = GetNextVisibleItem( hti );
}
}
return;
}
CTreeCtrl::OnTimer(nIDEvent);
}
void CTreeCtrlEx::OnNcMouseMove(UINT nHitTest, CPoint point)
{
//Since most tree controls have that nice client edge border.
//If the user moves the mouse from
//bottom to top, after passing over the first visible item will
//leave the underline. So we have to
//handle WM_NCMOUSEMOVE for when it goes over the border of the
//tree control...
if( nHitTest == HTBORDER )
{
HTREEITEM hti = GetFirstVisibleItem();
if( GetItemState( hti, TVIS_UNDERLINE) & TVIS_UNDERLINE )
SetItemState( hti, 0, TVIS_UNDERLINE );
}
CTreeCtrl::OnNcMouseMove(nHitTest, point);
}
In the above code, I could unconditionally set the item state, but
SetItem ( which is called internally by SetItemState ) triggers an
invalidate, and there is no reason to redraw if we don’t have to.
Now that we are setting the state properly…how do we go about drawing
the underline? Simple…do it the same way that another sample does it.
That sample that I based my drawing code on is – Setting Color and Font
Attributes for individual items.
Here is my WM_PAINT handler…
void CTreeCtrlEx::OnPaint()
{
CPaintDC paintDC(this);
CRect clientRect(-1,-1,-1,-1);
GetClientRect(&clientRect);
CDC memDC;
memDC.CreateCompatibleDC( &paintDC );
CBitmap canvas, *pOldCanvas = NULL;
canvas.CreateCompatibleBitmap( &paintDC, clientRect.Width(), clientRect.Height() );
pOldCanvas = memDC.SelectObject( &canvas );
CRect clipBox(-1,-1,-1,-1);
paintDC.GetClipBox(&clipBox);
CRgn clipRgn;
clipRgn.CreateRectRgnIndirect(&clipBox);
memDC.SelectClipRgn( &clipRgn );
CWnd::DefWindowProc( WM_PAINT, (WPARAM)memDC.m_hDC, 0 );
HTREEITEM hti = GetFirstVisibleItem();
int iVizCount = GetVisibleCount() + 1;
while( hti && iVizCount-- )
{
BOOL bUnderline = !!(GetItemState( hti, TVIS_UNDERLINE ) & TVIS_UNDERLINE);
UINT flags = TVIS_SELECTED|TVIS_DROPHILITED;
if( (GetItemState( hti, flags ) & flags) == 0 )
{
CFont* pTreeFont = GetFont();
if( pTreeFont == NULL )
pTreeFont = CFont::FromHandle( (HFONT)::GetStockObject(DEFAULT_GUI_FONT) );
ASSERT_VALID(pTreeFont);
LOGFONT lfTree;
::ZeroMemory(&lfTree, sizeof(lfTree));
pTreeFont->GetLogFont(&lfTree);
if( bUnderline )
lfTree.lfUnderline = TRUE;
CFont font;
font.CreateFontIndirect(&lfTree);
CFont* pOldFont = memDC.SelectObject(&font);
CString sItemText = GetItemText( hti );
CRect itemRect(-1,-1,-1,-1);
GetItemRect( hti, itemRect, TRUE );
COLORREF clrOld = 0;
if( bUnderline )
clrOld = memDC.SetTextColor( ::GetSysColor(COLOR_GRAYTEXT) );
memDC.TextOut( itemRect.left + 2, itemRect.top + 1, sItemText );
if( bUnderline )
clrOld = memDC.SetTextColor( clrOld );
memDC.SelectObject( pOldFont );
}
hti = GetNextVisibleItem( hti );
}
paintDC.BitBlt( clipBox.left, clipBox.top, clipBox.Width(),
clipBox.Height(), &memDC, clipBox.left, clipBox.top, SRCCOPY );
memDC.SelectObject( pOldCanvas );
}
